The proposed research investigates the role of the efferent system in protecting the eight nerve. Noise, ischemia, and excitatory neurotransmitter-infusion result in similar pathophysiological processes. The efferent system provides protection against at least two of these traumatic insults. In Specific Aim 1, we will test the hypothesis that lateral efferent pathways mediate sound-induced trauma in guinea pigs. We will lesion the lateral superior olive, the origin of lateral efferent fibers, then expose subjects to loud sounds. Lesioned subjects should show more sound-induced damage. Sound-induced functional deficits will also be assessed during cochlear perfusion with lateral efferent neurotransmitters. Perfusion of these neurotransmitters should reduce deficits. In Specific Aim 2, we will test the hypothesis that activation of the efferent system with non-=traumatic acoustic stimulation results in protection against excitatory neurotransmitter-induced trauma. Protective mechanisms will be specifically linked to the efferent pathways when we conduct efferent lesions, and infuse lateral efferent neurotransmitters. Understanding protection by the efferent system may lead to the identification of methods for protecting the auditory system. If we can identify protection mechanisms at a molecular level, we may be able to up- regulate or apply exogenous factors in clinical settings to provide protection to those know they will be exposed to potentially damaging stimulation. Similar treatment could be provided for those likely to undergo periods of transient ischemia during surgical procedures involving the eighth nerve.